The present invention relates to a new and improved construction of control circuit for an apparatus for adjusting and dressing a dished or plate-shaped grinding wheel, and which is of the type containing a feeler or sensor which can be periodically brought into contact at one feeler end with the grinding wheel, wherein the other feeler end acts by means of an operative connection upon a control circuit.
According to a prior art apparatus for dressing a grinding wheel at a gear wheel-grinding machine, for instance as disclosed in the commonly assigned U.S. Pat. No. 4,213,277, granted July 22, 1980 and the corresponding German patent publication No. 2,724,843, published Nov. 9, 1978, for the periodic dressing of a planar ring-shaped portion or active rim of a dished or plate-shaped grinding wheel which can be axially repositioned there is controlled the position of the active rim of the grinding wheel and such grinding wheel is repositioned such that the active rim or ring-shaped portion remains positioned at the same site independent of its wear. This active rim is dressed one respective time within a preselected dressing interval by means of a likewise axially adjustable dressing tool. For this purpose there is provided a control circuit equipped with a feeler contact attached to a feeler or sensor. The feeler is intermittently applied to the active rim of the grinding wheel and, as soon as the feeler contact is closed in response to a certain wear of the active rim, the control circuit delivers a command for the readjustment or compensating feed of the grinding wheel This compensating feed is accomplished in each instance through the spacing of one tooth of a ratchet wheel, by means of which there can be positionally adjusted the grinding wheel spindle. If within a preselected dressing interval there is not attained a predetermined number of compensating feeds, then this is interpreted as an indication that the surface of the grinding wheel is smudged or clogged, i.e. clogging of its pores by grinding dust, oil and so forth, and that the grinding wheel has not performed its proper grinding operation within a dressing interval. Thus, in this case the control circuit delivers a further command, by means of which a dressing tool is advanced by one tooth of a further ratchet wheel, and thereafter the dressing tool is pivoted over the active rim of the grinding wheel for dressing such grinding wheel.
With this state-of-the-art equipment the scanning of the grinding wheel is only intended for accomplishment of the compensating feed or readjustment of the grinding wheel since the dressing operation always remains constant and only then is initiated if, within a dressing interval, there has not been attained the preselected number of grinding wheel-compensating feeds or readjustments. What can be considered to be capable of improvement with this equipment operation is that the feeling or scanning operation delivers no information or data regarding the quality of the grinding wheel, i.e. it is not possible to draw any conclusions regarding the appearance of its grinding surface. Additionally, during the dressing operation always the same amount of material is removed from the grinding wheel without really knowing whether such material removal is even absolutely needed. Moreover, since the feeler contact only delivers a Yes/No-information, i.e. whether the grinding wheel is to be readjusted or not, it is not possible to determine to what extent the grinding wheel spindle is to be fed or readjusted in each case. It is for this reason that with such prior art equipment the grinding wheel spindle is simply always positionally adjusted through one tooth of the ratchet wheel. Whether or not such compensating feed is adequate or too great only can be determined during the next feeling or scanning interval.
When the active rim of a grinding wheel, following a number of compensating feeds, has reached a certain axial minimum dimension by virtue of the dressing work, then the danger exists that the grinding wheel tends to bend because of the grinding pressure which is exerted, and thus, produces unsatisfactory grinding results. Therefore, it is necessary to adjust the grinding wheel in radial direction, so that its jacket or outer surface can be dressed by a further dressing device. The prior art equipment furnishes no data as to the point in time when such radial adjustment of the grinding wheel, and thus, dressing of its outer or jacket surface is to take place.
Moreover, it is generally possible in the case of grinding machines that the operator manually readjusts the grinding wheel spindle. At a grinding machine equipped with a conventional apparatus known in this technology, should the grinding wheel spindle be readjusted manually to too great an extent, then the dressing tool will unnecessarily remove too much material from the grinding wheel. This reduces the service life of the grinding wheel. The same drawback occurs when the grinding wheel, with automatic compensating feed or advance, is too frequently positionally readjusted during a dressing interval, because then the grinding wheel is dressed too often and then again must be readjusted through one ratchet wheel tooth.